The present invention relates to disk array storage devices such as RAID (Redundant Array of Inexpensive Disk), etc. using a plurality of disk memories and more particularly to storage data reading methods from disk array memories and control devices. The RAID system storage disclosed in U.S. Pat. No. 5,124,987, Japanese Patent No. 214720/1994 and 266510/1994, proposes a high speed writing method to memories. A method to write updated-data collectively in previously arranged separate empty areas in disk memory units (hereinafter simply referred to as disk memory units) instead of rewriting old data areas and a rewriting method of old data areas in idle times when made available thereafter were proposed.
The conventional methods described above will be briefly described using FIG. 18. In FIG. 18, an example involving updating data blocks stored in logic block addresses (hereinafter simply referred to as logic addresses) L6, L4, L2, L132, L7 and L11 is considered. In these logic block addresses L6, L4, L2, L12, L7 and L11, old data is stored in physical block addresses (hereinafter simply referred to as physical addresses) P6, P4, P2, P12, P7 and P11 in 3 disk units 181, 182 and 193. First, the data blocks 16Data, L4Data, L2Data, L12Data, L7Data and L11Data that are newly to be updated are stored temporarily in a buffer memory 184 which is normally composed of a non-volatile memory. These data blocks are collectively written into physical addresses P51, P52, P53, P54, P55 and P56 which are previously arranged separate empty areas instead of directly replacing data that are the contents of the physical block addresses P6, P5, P2 and P12 in which old data to be updated are stored, with old data left therein. As these data are written into continuous physical addresses P51-P52, P53-P54 and P55-P56 in 3 disk units 181, 182 and 183, 6 times of writing operation required for the direct rewriting are physically reduced to 3 times of the writing operation and thus, the writing performance is largely improved.
On the other hand, in this type of conventional disk array storage systems, there is provided a conversion map 185, that is a table showing the correspondence between logical addresses and physical addresses in which data blocks are stored. When updating data, as latest data in the logical addresses L6, L5, L2, L12, L7 and L11 are actually existing in the physical addresses P51, P52, P53, P54, P55 and P56 in the disk units as described above, the contents of the conversion map are rewritten to indicate proper disk locations. In other words, for instance, data blocks in the logical address L6 must originally be stored in the physical address P6 in the disk unit 181 but as actually they are stored in the physical address P51, the physical address P6 corresponding to the logical address L6 in the conversion map 185 is rewritten to P51. Similarly, the physical addresses corresponding to the logical addresses L5, L2, L12, L7 and L11 in the conversion map 185 are rewritten to P52, P53, P54, P55 and P56, respectively.
Further, when reading data stored in the disk array storage, data is read out by obtaining physical addresses wherein latest data blocks corresponding to designated logical addresses are stored are read out and therefore, there is no possibility to read out old data.
Further, in order to make the explanation simple, although only two physical blocks were written in the example shown in FIG. 18 as data blocks that are stored in one disk unit, several ten blocks are actually written in one disk unit.